The healing surge loss when the summoning dies is an incentive to dismiss the creature before it dies, as I see it. Wizards (and ranged people in general) get hit the least as well, so they're using less of their healing surges. Unless the party is getting hammered, or something slips past the defender for a long while, I don't think the surge death-tax is going to cause the party to rest on it's own. Generally, it's the defender's surges that determine when the party quits.